Optical transceiver tester

ABSTRACT

In embodiments of the present invention, an optical device tester performs stressed eye testing on several optical receivers and transmission and dispersion penalty testing on optical transmitters at a variety of data rates wavelengths using single mode optical signals and multimode optical signals using a variety of supply voltages and temperatures.

BACKGROUND

1. Field

Embodiments of the present invention relate to optical transceivers and,in particular, to testing optical transceivers.

2. Discussion of Related Art

Optical transmitter-receiver pairs, or transceivers, may be used incommunication systems and/or networks to transmit and receive dataand/or other information on optical signals. To ensure proper operation,optical transceiver performance may be tested. Traditional opticaltransceiver testing has limitations, however.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like reference numbers generally indicate identical,functionally similar, and/or structurally equivalent elements. Thedrawing in which an element first appears is indicated by the leftmostdigit(s) in the reference number, in which:

FIG. 1 is a high-level block diagram of an optical device testeraccording to an embodiment of the present invention;

FIG. 2 is a graphical representation of an optical signal according toan embodiment of the present invention;

FIG. 3 is a graphical representation of an optical signal according toan alternative embodiment of the present invention;

FIG. 4 is a flowchart illustrating an approach to operating an opticaldevice test system according to an embodiment of the present invention;

FIG. 5 is a graphical representation of test parameters for an opticaldevice test system according to an embodiment of the present invention;and

FIG. 6 is a high-level block diagram of a test system according to anembodiment of the present invention.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

FIG. 1 is a high-level block diagram of an optical transceiver tester100 according to an embodiment of the present invention. In theillustrated embodiment, the system 100 includes an optical signalgenerator 102 coupled to an optical switch 104. The illustrated opticalswitch 104 is coupled to several slots or bays 106 (such as, for exampleslots 106A, 106B, 106C, 106D, 106E, 106F, . . . 106N) wheredevices-under-test (DUT) may be installed or inserted. The illustratedslots 106 are coupled to a second optical switch 108. The illustratedoptical switch 108 is coupled to test instrumentation 110. In theillustrated embodiment, software 112 is coupled to the optical signalgenerator 102.

In the illustrated embodiment, the optical signal generator 102 includesan electrical signal generator 114 coupled to a light source 116. Theexample optical signal generator 102 also may include a clock 115coupled to the electrical signal generator 114, a jitter generator 118coupled to the electrical signal generator 114, and a second jittergenerator 120 coupled to a mixer 122.

In the illustrated embodiment, the optical switch 108 is coupled to andispersion module 140, which is coupled to the instrumentation 110. Theillustrated dispersion module 140 includes a transversal filter 141, afiber spool 142, and a second fiber spool 144.

In the illustrated embodiment, the light source 116 includes severallasers. For example, the illustrated light source includes an 850nanometer (850 nm) laser 146, a 1310 nm laser 148, and a 1550 nm laser150.

In the illustrated embodiment, a variable power supply 152 is coupled tothe slots 106. Also in the illustrated embodiment, a thermal chamber 154is coupled to the slots 106.

In embodiments of the present invention, the optical signal generator102 components may operate as follows. The electrical signal generator114 may generate a data stream 124. The data stream 124 may include apseudorandom bit sequence. The example pseudorandom bit sequence may bea PRSB-31, which may include 2³¹−1 (or approximately 2.1 billion) bitsand that may repeat every two seconds at one Gbps or every twentyseconds at ten Gbps. Alternatively, the pseudorandom bit sequence may bea PRSB-7, which may include 2⁷−1 (or approximately 127) bits and thatmay repeat many times per second at one Gbps or at ten Gbps.

The clock 115 may provide a clock signal to the electrical signalgenerator 114 to control the data rate of the data stream 124. Forexample, the clock 115 may provide a clock signal having a frequency inthe range of approximately fifty megahertz (50 MHz) to approximately tengigahertz (10 GHz) or greater, for example, from a clock 115, togenerate the data stream 124. In one embodiment, the clock signalprovides a 1.25 GHz clock signal to the electrical signal generator 114,which in response generates the data stream 124 having a data rate of2.5 Gbps. In an alternative embodiment, the clock signal provides a 5GHz clock signal to the electrical signal generator 114, which inresponse generates the data stream 124 having a data rate of ten Gbps.

In one embodiment, the data stream 124 may be applied to the lightsource 116 to the light source 116, which may convert the electricalsignal to an optical signal 130. FIG. 2 is a graphical representation(or eye diagram 200) of the optical signal 130 according to anembodiment of the present invention.

In one embodiment, the eye diagram 200 may include the data bitsacquired from the data stream 124 overlaid on top of each other. In theillustrated embodiment, the optical signal 130 includes a direct current(DC) bias level 202, which may be representative of average opticalpower in the optical signal 130, an amplitude 204, which may berepresentative of a logic level “1” for the optical signal 130, and anamplitude 206, which may be representative of a logic level “0” for theoptical signal 130.

In one embodiment, the eye diagram 200 may be acquired and viewed usingthe test instrumentation 110 using, for example, a general-purposeinterface bus (GPIB). In the illustrated embodiment, the optical signal130 includes a clean optical signal and the eye in the eye diagram 200is substantially open.

In an alternative embodiment, the optical signal generator 102 generatesan intentionally impaired or intentionally distorted optical signal 131.For example, jitter 132 may applied to the electrical signal generator114 to introduce the jitter in the data stream 124 and the mixer 122 maymix the impaired data stream 124 with jitter 134. In embodiments of thepresent invention, jitters 132 and or 134 may be horizontal jitter,timing jitter, sine jitter, sine interference, vertical jitter, and/oramplitude jitter.

The resulting electrical signal 136 having the data stream 124 impairedby the jitter 132 and 134 may be applied to the light source 116 togenerate an intentionally impaired or intentionally distorted opticalsignal 131. FIG. 3 is a graphical representation (or eye diagram 300) ofthe optical signal 131 according to an embodiment of the presentinvention in which the eye in the eye diagram 300 is somewhat closed orstressed. In one embodiment, the closure or stress on the eye in the eyediagram 300 may be an indication that there are bit errors in the datastream 124 caused by introducing jitter 132 and 134 into the data stream124.

Like the eye diagram 200, the eye diagram 300 may include the data bitsacquired from the data stream 124 overlaid on top of each other, and theoptical signal 130 includes a direct current (DC) bias level 302, anamplitude 304, and an amplitude 306.

Referring back to FIG. 1, in the illustrated embodiment, the opticalswitch 104 couples the optical signal 130 to the instrumentation 110 andthe optical signals 130 and 131 to individual slots in the slots 106.The optical switch 104 may include a 1×10 optical switch, a 1×8 opticalswitch, or several optical switches that couple the optical signal 130to the instrumentation 110 and the optical signal 131 to individualslots in the slots 106.

An individual slot 106 may be any suitable slot or bay that may receivean optical device. In embodiments of the present invention, anindividual slot 106 may receive optical devices such as, for example,transmitters, receivers, transceivers, transmitter-receiver pairs,and/or transponders. Such optical devices may include, for example,devices compatible with the Institute of Electrical and ElectronicsEngineers (WEE) 802.3ae standard, IEEE std. 802.3ae- 2002, published2002. For example, one or more of the individual slots 106 may bepopulated with devices of the XFP family of devices, the XENPAK familyof devices, and/or X-Pak family of devices. Alternatively, 300-pinmulti-source agreement (MS A) lO Gigabit Ethernet (1OGbE) opticaldevices may be disposed in one or more of the individual slots 106.

In the illustrated embodiment, the optical switch 108 couples an opticalsignal 133 from the individual slots in the slots 106 to theinstrumentation 110 and couples the optical signal 130 from theindividual slots 106 to the dispersion module 140. The optical switch108 may include a 10×1 optical switch, an 8×1 optical switch, or severaloptical switches that couple the optical signal 133 to theinstrumentation 110 and/or the dispersion module 140.

The instrumentation 110 may be any suitable instrumentation that canmeasure optical signal power levels, electrical signal power levels, bitrates, wavelengths, voltages, and/or other parameters. In embodiments ofthe present invention, the instrumentation 110 may include any one or acombination of an oscilloscope, a digital communications analyzer, a biterror rate tester, a signal analyzer, and/or an error performanceanalyzer.

In one embodiment, the software 112 may include a graphically userinterface (GUI) written on top of Microsoft Windows® operating system,for example, that a test operator may use to input parameters for one ormore tests to be conducted on devices in the slots 106. The software 112may be interfaced with other components in the tester 100 usinggeneral-purpose interface bus (GPIB), for example.

In one embodiment, the electrical signal generator 114 may be anysuitable instrumentation and/or circuitry that can generate a variety ofpseudorandom bit sequences, such as, for example, PRBS 2³¹−1, PRBS2²³-1, PRBS 2¹⁵−1, PRBS 2¹⁰−1, and/or PRBS 2⁷-1, or other suitable bitsequence, over a range of bit rates and/or clock frequencies.

The light source 116 may be suitable laser, such as, for example, alaser diode, that can convert an electrical signal to an optical signal.In embodiments of the present invention, the 850 nm laser 146 may be amultimode laser, the 1310 nm laser 148 may be a single mode laser, andthe 1550 nm laser 150 may be a single mode laser.

In one embodiment, the jitter generator 118 may be any suitableinstrumentation and/or circuitry that can generate timing jitter and/orhorizontal jitter, the jitter generator 120 may be any suitableinstrumentation and/or circuitry that can generate amplitude jitterand/or vertical jitter, and the mixer 122 may be any suitable deviceand/or circuitry that can combine the jitter 132 and 134 with the datastream 124. In one embodiment, the mixer 122 may be a radio frequency(RF) mixer.

In one embodiment, the optical fiber spool 142 may include single modeoptical fiber having a length of approximately forty kilometers. In oneembodiment, the optical fiber spool 144 may include single mode opticalfiber having a length of approximately ten kilometers. In theillustrated embodiment, an optical signal 135 is coupled between thedispersion module 140 to the instrumentation 110.

FIG. 4 is a flowchart illustrating a method 400 of operating of thetester 100 according to an embodiment of the present invention. Themethod 400 begins with a block 402 in which a test operator may inputtest parameters into the tester 100, using the GUI of the software 112,for example, for the tester 100 to implement.

FIG. 5 is a graphical representation 500 showing example parameters tobe entered into the tester 100. In the illustrated embodiment, thegraphical representation includes a column 502 listing the slot to beselected. In the illustrated embodiment, the graphical representationincludes a column 504 listing the device to be installed in the selectedslot.

In the illustrated embodiment, the graphical representation includes acolumn 506 listing the type of test to be performed on the device. Onetype of test may be a stressed eye test in which an optical signal isstressed in a deterministic manner, such as the optical signal 131, forexample, is applied to a receiver to test the receiver's performanceunder non-ideal conditions.

Another type of test may be a transmitter and dispersion penalty (TDP)test in which an optical signal that has not been intentionallydistorted, such as the optical signal 130, for example, is applied to areceiver and a transmitter and is retransmitted through dispersiondevices, such as the dispersion module 140, or a transversal filter (notshown), for example.

In the illustrated embodiment, the graphical representation includes acolumn 508 listing the type of test result expected after a test isperformed. For example, a receiver's performance may be evaluated bymeasuring the bit error rate of the optical signal out of the receiver,such as the bit error rate (BER) of the optical signal 133.Alternatively, the receiver's performance may be evaluated bydetermining whether the receiver passed or failed a particular test,such as failure to meet a predetermined bit error rate.

A transmitter's performance may be evaluated by comparing the opticalmodulation amplitude (OMA) of a reference optical signal, such as forexample, the optical signal 130, with the OMA of the optical signaloutput from the device under test, such as for example, an opticalsignal 135, which is output from the dispersion module 140. In oneembodiment, the OMA may be the difference in optical power levels forthe logic level “1” and logic level “0” of the optical signal 130 andthe optical signal 135.

In the illustrated embodiment, the graphical representation includes acolumn 510 listing whether the optical signal 130 and/or 131 are to besingle mode or multimode.

In the illustrated embodiment, the graphical representation includes acolumn 512 listing operating wavelengths in nanometers.

In the illustrated embodiment, the graphical representation includes acolumn 514 listing bit rates in Gbps.

In the illustrated embodiment, the graphical representation includes acolumn 516 listing a voltage range, which may be a percentage of thesupply voltage to the devices in the slots 106 as provided by thevariable power supply 152.

In the illustrated embodiment, the graphical representation includes acolumn 518 listing a temperature range to which the devices in the slots106 may be subjected during testing as provided by the thermal chamber154.

The listing of parameters in FIG. 5 is not exhaustive and in embodimentsof the present invention, the test operator also may input otherparameters as well such as receiver manufacturer and test sequence, forexample, whether to test all the receivers first, then the transmitters,whether to perform the single mode test first and the multimode testssecond, whether to group the testing based on operating wavelength, etc.For purposes of illustration, we will assume that the sequence is slot106A, slot 106B, slot 106C, slot 106D, slot 106E, slot 106F, and slot106N.

Referring back to FIG. 4, in a block 404, in response to the testoperator inputs the software 112 may initialize tester 100 and cause thetester 100 to perform the blocks below without operator intervention. Inone embodiment, the software 112 may initialize the tester 100 usingprevious calibration settings, for example.

In a block 406, the tester 100 tests the receiver in the slot 106A. Inone embodiment, the software 112 may cause the optical signal generator102 to generate the optical signal 131 as a single mode optical signalhaving a wavelength of 1310 nanometers and a bit rate of 0.5 Gbps, theoptical switch 104 to switch the optical signal 131 to the slot 106A sothat a stressed eye test may be performed on the receiver in the slot106A, the optical switch 108 to couple the optical signal 133 to theinstrumentation 110, and the instrumentation to indicate whether thereceiver in the slot 106A passed or failed the stressed eye test. In oneembodiment, the instrumentation 110 may store the results of the test.

In a block 408, the tester 100 tests the receiver in the slot 106B. Inone embodiment, the software 112 may cause the optical signal generator102 to generate the optical signal 131 as a single mode optical signalhaving a wavelength of 1550 nanometers and a bit rate of one Gbps, theoptical switch 104 to switch the optical signal 131 to the slot 106B sothat a stressed eye test may be performed on the receiver in the slot106B, the optical switch 108 to couple the optical signal 133 to theinstrumentation 110, and the instrumentation to indicate the bit errorrate of the receiver in the slot 106B. In one embodiment, theinstrumentation 110 may store the results of the test.

In a block 410, the tester 100 tests the receiver in the slot 106C. Inone embodiment, the software 112 may cause the optical signal generator102 to generate the optical signal 131 as a multimode optical signalhaving a wavelength of 850 nanometers and a bit rate of two Gbps, theoptical switch 104 to switch the optical signal 131 to the slot 106C sothat a stressed eye test may be performed on the receiver in the slot106C, the optical switch 108 to couple the optical signal 133 to theinstrumentation 110, and the instrumentation to indicate whether thereceiver in the slot 106C passed or failed the stressed eye test. In oneembodiment, the instrumentation 110 may store the results of the test.

In a block 412, the tester 100 tests the transmitter in the slot 106D.In one embodiment, the software 112 may cause the optical signalgenerator 102 to generate the optical signal 130 as a single modeoptical signal having a wavelength of 1310 nanometers and a bit rate offive Gbps, the optical switch 104 to switch the optical signal 130 tothe instrumentation 110 and to the slot 106D, the optical switch 108 tocouple the optical signal 137 from the slot 106D to the dispersiondevice 140, and the instrumentation 110 to indicate whether the receiverin the slot 106D passed or failed the TDP test by comparing the OMA ofthe optical signal 135 to the OMA of the optical signal 130, forexample. In one embodiment, the instrumentation 110 may store theresults of the test.

In a block 412, the tester 100 tests the transmitter in the slot 106D.In one embodiment, the software 112 may cause the optical signalgenerator 102 to generate the optical signal 130 as a single modeoptical signal having a wavelength of 1310 nanometers and a bit rate offive Gbps, the optical switch 104 to switch the optical signal 130 tothe instrumentation 110 and to the slot 106D, the optical switch 108 tocouple the optical signal 135 from the slot 106D to the dispersiondevice 140, and the instrumentation 110 to indicate whether the receiverin the slot 106D passed or failed the TDP test by comparing the OMA ofthe optical signal 135 to the OMA of the optical signal 130, forexample. In one embodiment, the instrumentation 110 may store theresults of the test

In a block 414, the tester 100 tests the transmitter in the slot 106E.In one embodiment, the software 112 may cause the optical signalgenerator 102 to generate the optical signal 130 as a single modeoptical signal having a wavelength of 1550 nanometers and a bit rate often Gbps, the optical switch 104 to switch the optical signal 130 to theinstrumentation 110 and to the slot 106E, the optical switch 108 tocouple the optical signal 135 from the slot 106E to the dispersiondevice 140, and the instrumentation 110 to indicate whether the receiverin the slot 106E passed or failed the TDP test by comparing the OMA ofthe optical signal 135 to the OMA of the optical signal 130, forexample. In one embodiment, the instrumentation 110 may store theresults of the test.

In a block 418, the tester 100 tests the receiver in the slot 106F. Inone embodiment, the software 112 may cause the optical signal generator102 to generate the optical signal 131 as a single mode optical signalhaving a wavelength to 1330 nanometers and a bit rate of twenty Gbps,the optical switch 104 to switch the optical signal 131 to the slot 106Fso that a stressed eye test may be performed on the receiver in the slot106F, the optical switch 108 to couple the optical signal 133 to theinstrumentation 110, the instrumentation to indicate the bit error rateof the receiver in the slot 106F, and the stressed eye test to beperformed a first, second, and third time as supply voltage to the slot106F is changed from a first value, a second value, and a third value,respectively, to determine the bit error rate at the first, second, andthird values, respectively. In one embodiment, the instrumentation 110may store the results of the test.

In a block 418, the tester 100 tests the receiver in the slot 106N. Inone embodiment, the software 112 may cause the optical signal generator102 to generate the optical signal 131 as a single mode optical signalhaving a wavelength of 1550 nanometers and a bit rate of twenty-fiveGbps, the optical switch 104 to switch the optical signal 131 to theslot 106N so that a stressed eye test may be performed on the receiverin the slot 106N, the optical switch 108 to couple the optical signal135 to the instrumentation 110, the instrumentation to indicate the biterror rate of the receiver in the slot 106N, and the stressed eye testto be performed a first, second, and third time as the temperature ofthe slot 106F is changed from a first value, a second value, and a thirdvalue, respectively, to determine the bit error rate at the first,second, and third values, respectively. In one embodiment, theinstrumentation 110 may store the results of the test.

The operations of the method 400 have been described as multiplediscrete blocks performed in turn in a manner that may be most helpfulin understanding embodiments of the invention. However, the order inwhich they are described should not be construed to imply that theseoperations are necessarily order dependent or that the operations beperformed in the order in which the blocks are presented. Of course, themethod 400 is an example process and other processes may be used toimplement embodiments of the present invention. A machine-accessiblemedium with machine-readable data thereon may be used to cause amachine, such as, for example, a processor to perform the method 400.

FIG. 6 is a high-level block diagram of a test system 600 according toan embodiment of the present invention. The illustrated test system 600includes the tester 100 coupled to a communications port 602 and a powersupply 604. In the illustrated embodiment, the communication port 602 iscoupled to a data collection server 606.

In one embodiment, the tester 100 sends the results of the testsperformed in the tester 100 to the data collection server 606, as datalogs and/or data collection files, for example. The data collectionserver 606 may send the results to a database (not shown).

In one embodiment, the communication port 102 may be an Ethernet port,such as a Gigabit Ethernet port. In alternative embodiments, thecommunication port 602 may be a modem, a telephone line, or othersuitable communication port.

Embodiments of the present invention may be implemented using hardware,software, or a combination thereof. In implementations using software,the software may be stored on a machine-accessible medium.

A machine-accessible medium includes any mechanism that may be adaptedto store and/or transmit information in a form accessible by a machine(e.g., a computer, network device, personal digital assistant,manufacturing tool, any device with a set of one or more processors,etc.). For example, a machine-accessible medium includes recordable andnon-recordable media (e.g., read only memory (ROM), random access memory(RAM), magnetic disk storage media, optical storage media, flash memorydevices, etc.), as recess as electrical, optical, acoustic, or otherform of propagated signals (e.g., carrier waves, infrared signals,digital signals, etc.).

In the above description, numerous specific details, such as, forexample, particular processes, materials, devices, and so forth, arepresented to provide a thorough understanding of embodiments of theinvention. One skilled in the relevant art will recognize, however, thatthe embodiments of the present invention may be practiced without one ormore of the specific details, or with other methods, components, etc. Inother instances, recess-known structures or operations are not shown ordescribed in detail to avoid obscuring the understanding of thisdescription.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, process, block,or characteristic described in connection with an embodiment is includedin at least one embodiment of the present invention. Thus, theappearance of the phrases “in one embodiment” or “in an embodiment” invarious places throughout this specification does not necessarily meanthat the phrases all refer to the same embodiment. The particularfeatures, structures, or characteristics may be combined in any suitablemanner in one or more embodiments.

The terms used in the following claims should not be construed to limitembodiments of the invention to the specific embodiments disclosed inthe specification and the claims. Rather, the scope of embodiments ofthe invention is to be determined entirely by the following claims,which are to be construed in accordance with established doctrines ofclaim interpretation.

1. An apparatus, comprising: a signal generator to generate a singlemode optical signal and a multimode optical signal, the single modeoptical signal and the multimode optical signal being intentionallyimpaired; and an optical switch to switch the single mode optical signaland the multimode optical signal to a slot, the slot to be populatedwith a transceiver to be tested using the single mode optical signal andthe multimode optical signal.
 2. The apparatus of claim 1, furthercomprising a power supply to supply a first supply voltage and a secondsupply voltage to the first and/or the second slot, the first supplyvoltage being different from the second supply voltage.
 3. The apparatusof claim 2, further comprising a thermal unit to subject the firstand/or the second slot to a first temperature and a second temperature,the first temperature being different from the second temperature.
 4. Asystem, comprising: a tester having: a signal generator to generate asingle mode optical signal and a multimode optical signal, the singlemode optical signal and the multimode optical signal being intentionallyimpaired; and an optical switch to couple the single mode optical signaland the multimode optical signal to a slot, the slot to be populatedwith a receiver to be tested using the single mode optical signal andthe multimode optical signal; and a communication port to receiveresults of a test performed on the receiver.
 5. The system of claim 4,wherein the communication port comprises an Ethernet port.
 6. The systemof claim 5, wherein the communication port comprises Gigabit Ethernetport.